U67+L20B+L28 Flat Top Piston Compression

[BigW]

I was wondering what compression I’d get if I were put a u67 head on a l20b block bored 1mm over with l28 flat top pistons, thanks.

[datzenmike]

L20B bored 1mm to 87mm stock rod and crank, flattop pistons and un-shaved U67 head would be 10.11.

[banzai510(hainz)]

a motor that better run on 94 octane otherwise youll be replacing headgaskets or detonation issues

[Stoffregen Motorsports]

10:1 is perfectly fine on the street.

[banzai510(hainz)]

Stoff

I had a guy here who ran that set up and it pinged so bad, But in Washington we only get 91. He had to run a AV gas mix and 91 then it hauled ass

[Stoffregen Motorsports]

The last 510 I owned had a 2200 with 12:1. I ran it with a DGV and later with dual 44's. The timing was set at around 25 degrees and it made 210hp on pump gas. It ran so smoothly and never pinged at all.

[banzai510(hainz)]

You must have had a closed chamber head on yours.

I have a L16 flattops  w U67 head(521) and pings on regular so I got to run Super which cost more than the truck is worth.

I must be doing somethng wrong.

 

210hp is pretty impressive.

There was another guy who had a LZ power with electromotive timming coil packs and he pumped 140hp at the wheels.which is really pretty good.

[Stoffregen Motorsports]

It was a closed chamber head, but was opened up to match the 89mm bore and to unshroud the valves. The pistons were flat top KA24E in the beginning, but then swapped to cut down KA24DE dished pistons later.

[BigW]

Thanks for your replies, I really appreciate y’all spending your time on this post.

[distributorguy]

Pinging is controlled by setting up the right timing.  That doesn't infer changing the base timing setting with a stock distributor - it will need to be customized.  11:1 on a street motor is very much possible with no pinging.  You can go higher with the right cam.  10:1 is easy to tune for street use, and may not even require premium fuel.  Heck, many modern cars run 11:1.  

[john510]

Modern cars also have knock sensors and computer controlled ignition.An L series motor doesn't.

[datzenmike]

As well as complete control of fuel air mix and some engines are direct injection and compression doesn't really matter as much.

 

But that said, retarding the timing to prevent pinging produces less power than avoiding/eliminating pinging in the first place. Higher octane will allow you to increase the advance and be more efficient. Dual plug (NAPS) design will allow less advance to be used and get the same efficiency as single plug with more advance.

[Bastard_510]

well the biggest thing to stop detonation is matching your static compression with a cam duration that drops your effective compression to 7-7.5:1 theres a few calculators out there you can use. a 290ish duration cam should be perfect at 7.3:1 EC

[datzenmike]

Yes at low speeds. All engines have a lower compression (or effective compression) at lower engine speeds and at starting because the intake is open for about 1/4 of the way up the cylinder on the compression stroke. At higher engine speeds and high intake air speeds the cylinder will actually keep flowing into the cylinder even though the valve is open and the piston rising. This can easily exceed 100% volumetric efficiency, or the full swept volume of the cylinder, without a turbo or super charger. A 10 to one compression engine could effectively have 11 to one compression at extremely high RPMs.. High overlap and late closing intakes have shitty idle and low speed power because of this. 

[scooter]

I can tell you boys that 12.3:1 is too much, im down closer to 11:1 with a locked dizzy and i can get away with 94 now. NOT 91

i have a “huge ass cam” though and my car hates life below 3000 rpm

[Bastard_510]

1 hour ago, scooter said:

I can tell you boys that 12.3:1 is too much, im down closer to 11:1 with a locked dizzy and i can get away with 94 now. NOT 91

i have a “huge ass cam” though and my car hates life below 3000 rpm

I’m about to run 314 duration on 91 cam grinder confirm it will be just fine.  As for below 3k drive it like it was intended. Floor it, slip the clutch, hold a gear longer than normal. What’s the point in building something if you’re not going to enjoy it.

[datzenmike]

What differential gears?

[scooter]

13 hours ago, Bastard_510 said:

I’m about to run 314 duration on 91 cam grinder confirm it will be just fine.  As for below 3k drive it like it was intended. Floor it, slip the clutch, hold a gear longer than normal. What’s the point in building something if you’re not going to enjoy it.

You should be ok as you have a dish piston and a closed chamber head which helps. My motor is flat top with open chamber.

 

and yes, wail the fuck out of it thats how its driven. Also having a timing map (cb black box or crank trigger) setup can dramatically improve things.